1. Field of the Invention
The present invention relates generally to speed change gear systems and more particularly to a speed change gear system which is adapted for application with fluid couplings utilized within motor vehicles, especially automobiles.
2. Description of the Prior Art
It is preferable to utilize at least four gear sets within the speed change gear system of large automotive vehicles, such as for example, trucks and buses, and in order to attain a speed change mechanism having more than four speed shifts, three, four or even more sets of simple, signal-pinion or double-pinion type planetary gear sets have been heretofore combined. While the combination of these gears may be widely varied, it is preferable however that the following conditions be attained:
1. The output shaft should be coupled to the same elements within each speed range.
2. In order to reduce the circumferential speed of the bearing of each element of the planetary gear set, the number of its revolutions should be small.
3. The tooth load, that is, the tangential force of each element should be small so as to maintain the strength of the gear teeth.
4. The gear set should always attain meshing conditions for the number of teeth required. For example, the sun gear, whose diameter is to be minimized, as well as each planetary pinion gear, should have the necessary number of teeth.
5. Within the planetary gear set, the coupling relationship among the elements should be simple and the distance from each other should be small.
6. During speed shifts, wherein frictional coupling means are utilized during forward drive, such speed shifts should be available through one coupling means alone.